This invention relates to a pumping device of the type which is automatically started and stopped by means of a pressure switch adapted to sense the internal pressure of a pressure tank mounted on the delivery side of a pump, and more particularly it is concerned with an automatic pumping device of the type which is kept from being started and stopped often even if the size of the pressure tank for the pump is reduced.
Generally, an automatic pumping device comprises a pump, a pressure tank mounted on the delivery side of the pump for storing pumped-up water therein, and a pressure switch for automatically starting and stopping the pump by sensing an increase or decrease in the internal pressure of the pressure tank caused by the consumption of water. The pump is automatically started and stopped when a tap connected to the terminal end of the delivery system of the pump is opened and closed.
When the pump requires a pressure tank for automatically starting or terminating its operation, the capacity of the pressure tank for storing water under pressure therein tends to increase. This makes it necessary to increase the overall size of the pumping device including the pressure tank. Thus several proposals have hitherto been made to reduce the size of the pressure tank so as to obtain a compact overall size in an automatic pumping device.
In case the volume of water emitted and consumed through the tap is smaller than the volume of water delivered by the pump, the excess water corresponding to the difference between the volume of water emitted for consumption and the volume of water delivered by the pump would flow into the pressure tank and increase its internal pressure in a relatively short time interval when the size of the pressure tank is reduced. This would cause the pressure switch to sense an increase in the internal pressure of the pressure tank and stop the operation of the pump. Water would continue to flow through the tap even if the pump stops its operation, so that the internal pressure of the pressure tank would be quickly lowered. Upon the pressure being lowered to the level at which the pump is adapted to be started, the internal pressure of the pressure tank would be sensed by the pressure switch and the pump would be started again. Thus, if the volume of water consumed by opening the tap is small, the pump would be repeatedly started and stopped, causing changes to occur in the volume of water delivered by the pump. Thus automatic pumping devices of the prior art have the disadvantage of causing a damage to the pressure switch because it is often opened and closed when the pressure pump is reduced in size.
The aforementioned drawback of automatic pumps of the prior art having a pressure tank of the small size could be eliminated by providing a controller which, acting in response to the flow rate of water in the delivery system of the pump, opens and closes the inlet of the pressure switch which senses the pressure existing on the delivery side of the pump.
However, since the inlet of the pressure switch is opened and closed in this system by utilizing the rate of flow of water in the delivery system of the pump, it is impossible to increase the operation force with which the inlet of the pressure switch is opened and closed. This has made it imperative to reduce the size of the inlet of the pressure switch to no larger than about 2 millimeters in diameter.
This has a disadvantage in that, when the tap connected to the end of the delivery system of the pump is suddenly opened wide to emit water therethrough, resistance of a high magnitude would be offered to the flow of water ejected from the pressure switch through the small inlet, making it impossible for the pressure of water in the pressure switch to be quickly brought to the level of the internal pressure of the pressure tank in slaved relation.
Thus, even if the internal pressure of the pressure tank (the pressure existing on the delivery side of the pump) is brought to the level at which the pump is adapted to be started or lowered below that level as a result of the tap being opened, the pressure in the pressure switch would be unable to reach the aforementioned level quickly. Thus the time at which the pressure in the pressure switch reaches the level at which the pump is adapted to be started would lag behind the time at which the internal pressure of the pressure tank reaches the level at which the pump is adapted to be started.
As a result, the trouble of the starting of the pump being delayed and the water emitted through the tap being interrupted would occur. Also, when means is provided to open and close the inlet of the pressure switch to control the starting and stopping of the pump as aforementioned, the inlet of the pressure tank would be subjected to the pressure in the delivery system of the pump at all times. Such pressure would be high when the pump is in operation, so that it would be necessary to impart high strength to the pressure tank by increasing the thickness of its wall.
Under these circumstances, difficulty has been encountered in providing an automatic pumping device of the small-size pressure tank type which can be of value in actual practice.